Variable pulse width generator employing flip-flop in combination with integrator-differentiator network

ABSTRACT

A control for a three phase A.C. motor elevator drive in which direction and desired speed signals, as dictated by customer and user demand, are electronically processed to provide intermediate ramp control signals. A summing circuit which utilizes the intermediate ramp control signal and a signal from an elevator motor speed and direction sensing circuit has an output which determines and controls the voltage input, via electronic trigger controls to thyristor controlled power and reversing switching circuits in at least two channels of the three phase A.C. input to a three phase A.C. drive motor. The motor control circuit incorporates a high rate of off-on and phase reversing switching with phase angle control of voltage and current to provide interrelated variable A.C. power supply for both drive and braking of the elevator drive motor in both directions of movement of the elevator cab.

United States Patent [191 Bucek et al.

VARIABLE PULSE WIDTH GENERATOR EMPLOYING FLIP-FLOP IN COMBINATION WITHINTEGRATOR-DIFFERENTIATOR NETWORK Inventors: Jiri B. Bucek; James R.Shultz, both of York, Pa.

Assignee: Fincor, Inc., York, Pa.

Filed: Mar. 27, 1972 Appl. No.: 238,141

Related US. Application Data Division of Ser. No. 62,869, Aug. 11, 1970,Pat. No. 3,678,355.

US. Cl 307/265, 307/232, 307/234, 1

Int. Cl. H03k 1/18 Field of Search 307/232, 228, 234, 235, 307/229, 265

References Cited UNlTED STATES PATENTS 12/1965 Scott 307/228 7/1966Marcus 307/228 10/1966 Grindle 307/228 10/1970 Loewer 307/232 5/1971Cross 307/228 8/1971 Stempler 307/232 July 30, 1974 3,638,128 1/1972Downs 307/232 3,749,939 7/1973 Kuijk v 307/232 3,749,942 7/1973 Moses307/232 FOREIGN PATENTS OR APPLICATIONS 1,288,634 8/1960 Germany 307/232Primary Examiner-John S. Heyman [5 7] ABSTRACT A control for a threephase A.C. motor elevator drive in which direction and desired speedsignals, as dictated by customer and user demand, are electronicallyprocessed to provide intermediate ramp control signals. A summingcircuit which utilizes the intermediate ramp control signal and a signalfrom an elevator motor speed and direction sensing circuit has an outputwhich determines and controls the voltage input,

via electronic trigger controls to thyristor controlled power andreversing switching circuits in at least two channels of the three phaseA.C. input to a three phase A.C. drive motor. The motor control circuitincorporates a high rate of off-on and phase reversing switching withphase angle control of voltage and current to provide interrelatedvariable A.C. power supply for both drive and braking of the elevatordrive motor in both directions of movement of the elevator cab.

1 Claim, 10 Drawing Figures lNTEG RATOR wad:

PATENTEB W snm not 9 VARIABLE PULSE WIDTH GENERATOR EMPLOYING FLIP-FLOPIN COMBINATION WITH INTEGRATOR-DIFFERENTIATOR NETWORK This is adivision, of application Ser. No. 62,869, filed Aug. ll, 1970, now US.Pat. No. 3,678,355.

BACKGROUND OF THE INVENTION Most high-speed electric elevators whichcarry people use a DC. motor to raise and lower the cab according to thesupervisory control scheme. Practically all high-speed automatic as wellas nonautomatic, elevators made today convert the available A.C. to D.C.by a specially designed motor-generator set used with a variable voltage(Ward-Leonard) control system. Because of low starting torques, elevatorA.C. drive motors have been operated at relatively high speeds, beingconnected to the hoist sheaves through a gear reduction set. Some of thepreviously known polyphase A.C. elevator drive motors used two sets ofwindings, one for high speed and one for low speed, however shiftingspeeds in such systems result in a noticable jar to the passengers. Morerecent developments in A.C. motors, particularly the three phase solidrotor type, have resulted in controls by voltage regulating meansenabling operation at variable speeds from stall up to near synchronousspeed. One aspect which has enabled this is improving cooling techniquesused to dissipate the substantial heat generated while A.C. motors areoperated at low speeds as well as during electrical braking. An exampleof such a motor is shown in US. Pat. No. 2,764,704.

Variable speed A.C. motors have been used with controls using variablevoltage levels and reversing switching mechanisms responsive tomagneticamplifier triggering devices. A major drawback to use of suchsystems in personnel carrying elevators is an inherent lag in themag-amp trigger circuit operations which, while relatively smooth, doesresult in a noticable step during each change in speed. While that istolerated in construction hoists and dumb waiters, nevertheless it isobjectionable for use in high-speed elevators for people.

The present invention provides an A.C. motor con trol using solid statetechnique to acquire a tight, sophisticated control of motoracceleration, deceleration and programmed speed which, to all intentsand purposes, eliminates lag in motor response to change speed signalsin the control system. The desired result is instantaneous response inmotor power or electrical braking.

The control circuit in the present invention provides motor directionaland speed reference signals as voltages shaped into a smooth linear rampsummed with a feedback signal which is responsive to motor speed anddirection. The amplitude and polarity of the amplified error controlsthe current flow and reversing of phase rotation, respectively, in atleast two of the three phase motor inputs through fast responding, solidstate trigger circuits controlling thyristor switches. Motor directionand speed conditions are sensed by a special A.C. tachometer andfeedback circuit which feeds into the feed control circuit, as describedabove. The A.C. tachometer with a direction and speed sensing circuit isthe subject matter of and is fully disclosed in a copending applicationSer. No. 875,193, filed Nov. 10, 1969.

SUMMARY Accordingly, a primary object of the present invention residesin providing a novel A.C. motor elevator drive circuit for cooperationwith a conventional automatic high-speed elevator supervisory logicsystem to enable a motor output drive having smooth and substantiallyinstantaneous changes in speed regardless of load as a result ofcontinuous comparison of command and feedback signals. While the noveldrive circuit has been specifically developed for use with A.C. motorsto drive elevators, it can be readily adapted for use in otherapplications of A.C. motors with variable speed and reversingrequirements.

In conjunction with the foregoing object, the motor utilized is a threephase solid rotor motor, at least two of the input phase lines beingconnected through thyratron type (thyristor or SCR) switching circuitsto control current and to reverse the associated phase input lines formotor speed and direction control. Both positive input power and A.C.braking are selectively utilized through the switching circuits. Eachphase channel has independent thyristor circuits for up and for downsignals and each independent thyristor circuit has opposed or inverseparallel thyristors for regulating each half cycle and is controlled viaits own solid state trigger circuit. A master control responsive to thecondition demanded by elevator logic, e.g., elevator to go up one flooror multi-floors, will control acceleration, maximum speed, decelerationand stop via an infinitely variable smooth output ramp signal modifiedby motor speed and direction and directed in timed relation with thevarious phase cycles to the appropriate trigger circuits.

In conjunction with the foregoing object, the elevator logic signals,after appropriate shaping are modified by demand directional logicsignals, amplified and integrated with feedback signals from the motortachometer circuit to provide control signals to up or down triggercircuits which control the thyristor switching circuits for the motorinput phase channels.

Still another object resides in providing a universal solid statetrigger circuit which provides positive going output trigger pulses forturning on an independent thyristor for each half cycle of analternating phase load channel. The trigger circuit includes abi-stable, multivibrator circuit whose set and reset inputs arecontrolled by timing pulses derived from each half-cycle of the phaseinput to the controlled phase channel. Speed signals are compared,shaped and via AND gates and amplifier circuits provide cycle choppingtrigger output pulses for each one-half cycle to control current flowthrough thyristor circuits during each half-cycle of an input phase.

Safety electronic lock-out circuits are provided to prevent both the upand down channels from being turned on by trigger circuits at the sametime. Current sensing devices in both the up and down channels of atleast one of the switchable phases feed signal information back to thelock-out circuits in the control signal input connections to the triggercircuits. Further safety circuits constitute devices such as line chokesin the three phase motor power input lines to protect the thyristorsfrom line current surges.

These and other objects will appear as the description proceeds inconnection with the appended claims and the annexed, below-describeddrawings.

DESCRIPTION OF DRAWINGS FIG. 1 is a block diagram illustrating a controlcircuit for a three phase A.C. elevator motor in accord with the presentinvention.

FIGS. 2A through 2F taken together, as indicated by the small legendassembly block FIG. 2 on the sheet with FIG. 2A, is a schematic diagramshowing an elevator drive circuit in accord with the block diagram ofFIG. 1. Each sheet includes a small assembly legend showing the positionin which that specific sheet fits into the overall FIG. 2.

FIG. 3 is an exemplary wave form chart illustrating timed signals atvarious points in the trigger circuit.

FIG. 4 is a schematic diagram illustrating how a thyristor switchingcircuit and a single trigger board can be incorporated into the FIG. 2circuit for controlling the power supply conduction angle in the thirdphase of the three phase motor.

DESCRIPTION The present invention is described as incorporated in acontrol system for use with a three phase AC. motor elevator drive andeliminates the motor generator set used to convert AC. power to DC.power for operating a DC. elevator drive as is used in most high speedelevators. It is to be understood that the system can be used to controlother three phase AC. motor applications.

The control system for the A.C. motor drive involves starting, runningand stopping the elevator lifting motor in a manner which avoids thediscomfort of abrupt transitions in speed. The motor control will bedescribed primarily with reference to the block diagram seen in FIG. 1although specific references will, at times, be made to the circuitry inthe schematic drawing FIG. 2 and the timing chart of FIG. 3.

Elevator supervisory circuits are well-known and conventional. Suchparts of an elevator system are usually acquired or furnished separatefrom the motor control circuits, and include the master panels, cabcontrols which pre-determine which elevators go to which floors; orselectively determine maximum speeds for different run, i.e., singlefloor and multi-floor runs; provide floor landing level circuits, doorcontrol and controlled circuits; and elevator bank interrelatingcircuits. While some of the output terminal parts of the supervisorycontrols are shown in this disclosure, most of the elevtor systemcomponents, not related to the motor control, have not been included.

Although the control system can be applied to the motor control for eachelevator in a bank of elevators in a system, for purposes of simplifieddescription, the elevator system to which the motor control is appliedand described can be considered to be one with a single car serving twoor more landings.

The logic in the elevator supervisory system provides signals to themotor control system which determines whether the motor drive shouldmake the elevator start, stop, go up or down, what its maximum speedwill be during the run, and its levelling speed. Accordingly, thecontrol circuit of this invention is responsive to such command signalsfrom the elevator switching logic, and feedback signals representativeof the condition of the control system as well as of motor speed anddirection are integrated and correlated with such logic signals toprovide appropriate control of the motor.

Certain modifications of the various sub-circuits such as amplifiers,integrators, inverters and feedbacks as well as safety circuits will beobvious to the skilled electrician and are intended to be encompassed inthis invention. As disclosed, thyristor or silicon controlled rectifier(SCR) switching circuits are used to control the power level input tothe elevator motor as well as to reverse the motor input phase leads.Any equivalent solid state thyratron-like device, which may be operatedby the application of a suitable signal to a control electrode thereofand which may thereafter be deactivated only by disabling atransconductive path thereof, the control electrode being insensitiveonce activated by the control signal until the next succeeding disablingof-the transconductive path, can be used in place of the thyristors. Forexample, TRIACs if made to take the requisite current flow, couldreplace the inverse parallel connected thyristors used in each phasedirection channel of the exemplary disclosure.

SPECIFIC DESCRIPTION Referring to FIG. 1, an elevator run will beinitiated by the supervisory system by depressing a control but ton (notshown) in the elevator car or at a landing. This actuates the elevatorswitching logic 20 which produces a predetermined DC. voltage signal onits output 22, which is connected to and provides an input to thefunction generator error amplifier 24. The amplitude of the voltageoutput signal developed by switching logic control 20 will determine themaximum speed to which the car can accelerate during the desired run andthe slower levelling speed as the car approaches the selected landing.For multi-floor runs the elevator logic signal will have an amplitudewhich permits the elevator to accelerate to its highest speed. Forsingle floor runs the control voltage amplitude will be less, permittingacceleration to a fraction of the highest speed. The supervisory controlalso provides an output signal at other predetermined levels indicativeof approach or levelling speeds; also provides a signal indicative ofzero speed or stop condition and which applies and releases the elevatorfloor holding brake; and also provides via, up and down relays 26 and28, a direction control for elevator drive.

The output on line 30 from the function error amplifier 24 is integratedin a function generator 32 at an adjustable preset rate. As the functiongenerator signal on output 33 integrates upward in amplitude, thatoutput signal on a parallel connection 34 is fed back to the functionerror amplifier 24 to oppose the input signal at a summing junction. Theoutput signal of the function generator then remains at a levelindicative of desired speed until the elevator logic dictates otherwise.

The function generator output signal, designated as the output ramp, isfed on line 33 to the ramp switching circuit 36 which includes relaycontacts 26-1 and 28-1 which, depending upon which of the up and downrelays 26 and 28 is energized, provides a control signal to one or theother input of an amplifier/inverter stage 38. Depending on thecondition of the up-down relay contacts (FIG. 2A) in the ramp switchingcircuit 36, the inverter output signal will either be a positive ramp ora negative ramp.

Coupled directly to the three phase drive motor shaft is a two phaseA.C. tachometer 61 which supplies both motor speed and motor directioninformation to the system. An output signal proportional to motor speedis obtained by rectifying and combining the two phase tachometer output,as is fully described in the aforedescribed copending application. Thissignal is positive for one direction of rotation of motor 60 andnegative for the other direction of rotation. The polarity reversal isaccomplished by the tachometer switching circuit 50. The tachometerfeedback signal is fed to a summing junction 40 (FIG. 2A), at the inputto the error regulator amplifier 42.

The system can be best described in conjunction with an example. If theelevator'is programmed to go up one floor by the elevator switchinglogic, that condition will produce a positive going ramp of apredetermined amplitude as the output on line 39 from theamplifier/inverter stage 38. This signal is fed to the summing junction40 (FIG. 2A) at the input of the regulator amplifier 42. As waspreviously described, also fed to this same summing junction 40 is aD.C. feedback signal on line 44 from the tachometer switching circuit.The polarity of the tachometer feedback signal is determined by thetachometer direction sensing circuit 48 and tachometer switching circuit50, such that it will buck out the positive ramp on line 39 frominvertor 38 when the elevator is programmed to go up. When the elevatoris programmed to run the opposite direction, via the supervisory logicrelays 26 and 28, FIG. 2A, and associated up or down relay switchingcontacts 26-1 and 28-1 (FIG. 2A) and 26-2 and 28-2 (FIG. 2B) thepolarity of both of these signals is reversed and the tachometer signalwill still buck out the ramp from inverter 38.

The difference signal from this summing process, which can be positiveor negative, is amplified and inverted through the regulator amplifier42. In all cases if the output signal from the regulator amplifier 42 isnegative it is an effective up signal and if positive it is an effectivedown signal to the motor power controlling circuits. It should be notedthat an up signal from the regulator 42 will not necessarily drive theelevator up, but can be a braking signal during a downward elevatordrive. During a normal run the drive motor 60 might be receiving both upand down signals even though the elevator is moving in one direction.This provides the required control of the system.

A'three-phase power source (FIG. 2F), through suitable circuit brakersand switches, provides A.C. drive power and, via transformers andrectifier circuits provides power and timing for the control system. Themain lines for phases A, B and C, designated 62, 64 and 66, areconnected through thyristor control and switching circuits to thethree-phase input lines 68, 70 and 72 to motor 60. Each of at least twoof the main lines, e.g., phases A and C, can be selectively connected toan associated pair of the three input lines to the three-phase motor 60,or can be reversely connected to the same pair of input lines torespectively provide drive or braking power in both directions of motorrotation.

The three phase AC. input, via the transformer T,,, T and T and fullwave rectifier circuits as seen in FIG. 2C, provides a regulated D.C.supply for the control system. Center tapped secondaries in transformerphases A and C provide cycle timing signals used by the thyristortrigger circuits, as will be further described.

Phase A, via power line 62, connects through dual inverse parallelthyristor control circuits 74 and 76 to respective motor input leads 68and 72 and phase C, via line 66, connects through dual inverse parallelthyristor control circuits 78 and 80m respective motor input leads 72and 68. Each dual thyristor controlcircuit has two thyristors connectedinparallel, but in opposed directions to enable controlled current flowin both directions, i.e., during each half cycle, if an appropriatelytimed trigger pulse is applied to the control electrode of the thyristorfor that half cycle of that phase channel.

Circuit 74 includes inverse parallel thyristors 82 and 84 and isdesignated up control for phase A. Circuit 76 includes inverse parallelthyristors 86 and 88 and is designated the down control for phase A.Circuit 72 includes thyristors 90 and 92 in inverse parallel arrangementand is designated the up control for phase C. Circuit 80 includesthyristors 94 and 96 in inverse parallel arrangement and is designatedthe down control for phase C.

Each thyristor has trigger (or control) leads connected to associatedtrigger circuits, as will be more fully described hereinafter.

It is necessary to prevent both the up channel and the down channel ineach of the phase A and phase C 'cur rent supplies to both the A and Cphase windings of the motor 60 from being turned 'on at the same time.If that were to happen, the three-phase input line currents would becomeexcessively large, and possibly damage the thyristors in the up and downphase switching channels. To prevent that from happening, the motordrive or braking current is sensed by current transformers 100 and 102in the up and down channel of one of input phases A or C. The sensed upor down current The amplitude of the output signal from the error (orregulator) amplifier 42, the amplitude of which represents the variationin high or low motor speed relative to the desired speed, is connected,via line 112, through directional diodes D and D, as inputs to one orthe other of the lockout circuits 108 and 110 and thence, as permittedby one of the lockouts 108 or 110, to up trigger circuits 114 and 118 ordown trigger circuits 116 and 120. A negative or up signal on input 112,through diode D, provides a signal from the up lockout circuit 108, viaits amplifier 125 on parallel connection lines 122 and 124, to drive thetwo up channel trigger circuits 114 and directly, while a positive ordown signal from the regulator amplifier 42, through diode D to the downlockout l 10 providesa signal on' its output 126 which must be invertedthrough inverter amplifier 128 and thence, via parallel connection lines130 Rectified signals from the up and down channel current transformers100 (up) and 102 (down) ground any incoming signals to respectivelockout circuits 110 (down) and 108 (up), so the function error signalson line 112 can have no effect on the signal lockout amplifier ifcurrent is sensed in the down channel and vice versa. Each of thelockout amplifiers and 128 when subjected to a signal output willprovide an amplified output signal between fixed positive and negativelevels which, in the exemplary control system, is selected as from +l0Vto l0V. When either circuit 108 or 110 is locked out, or the errorsignal on line 112 is zero, the

respective amplifier of the circuit will transmit a maximum positivelevel signal, and for a full power error signalon line 1 12 (either fullnegative or full positive) the safety interlock output signal from theappropriate one or the other of amplifiers 125 or 128 will be fullnegative. Adjustable resistors 127 and 129 in the input circuits ofrespective interlock amplifiers 125 and 128 enable adjustment of theiroutputs for a zero signal input.

The safety interlock down output is parallel connected via lines 130 and132 to the two trigger circuits 116 and 120 of trigger boards 1 and 3(FIGS. 28 and 2E) to drive, in appropriate timed relationship to thephase cycles, the down thyristors (86 and 88) (94 and.

96) in each channel of the respective A and C phase input lines to motor60, to provide variable down power in two legs of the three-phase linepower connection to the motor. Similarly, the safety interlock up outputis parallel connected via lines 122 and 124 to the two trigger circuits114 and 118 of trigger boards 2 and 4 (FIGS. 2B and 2E) to drive, inappropriate timed relationship to the phase cycles, the up thyristors(82 and 84) (90 and 92) in each channel of the respective A and C phaseinput lines to motor 60 to provide variable up power in two legs of thethree-phase inputs to the motor.

TRIGGER BOARDS The trigger circuits 114, 116, 118 and 120 of respectivetrigger boards 1, 2, 3 and 4 are identical and the boards areinterchangeable. The circuit components are assembled on a printedcircuit board with plug-in terminals. For convenience in drawingdisclosure, boards 1, 2 and 3 are shown in block form and the triggerboard circuit 118, which is the same as the circuit for all triggerboards, is disclosed in detail for trigger board 4 (FIG. 2E). All boardshave identical plug-in terminals and similar letter references are shownfor comparison purposes on trigger boards 1, 2, 3 and 4. Terminals D, E,F, P, R and T are terminal connections to various voltage levels (asindicated on the drawing) from the power supply. Terminals N and Vprovide connections to selected phase channels for receiving cycletiming signals corresponding to the A.C. wave forms of the respectivephases. Terminal J provides the connection for the input control signal(from the safety interlocks) to the trigger board. Terminals X and Y areisolated output terminals for one-half cycle thyristor triggering, whileterminals C and B provide the isolated output circuit for the other halfcycle triggering of the opposed thyristor in the associated up or downthyristor switching device for that phase channel.

As will be hereinafter described, trigger board No. 5, in thealternative embodiment (see FIG. 4), which enables provision ofthyristor switching control of conduction angle in the third phase (B),is identical to the other trigger boards, although the control signalinput connection is slightly different.

A wave form timing chart for a trigger board is seen in FIG. 3. Thevoltage wave form at the top represents the sine wave for a specificA.C. phase channel applied to the thyristor switching device and to theprimary windings of the power supply transformer (T '1, or Tcorresponding to that phase. An associated center tap secondary for thatphase transformer provides a pair of independent sine wave signals, 180out of phase with each other, via connections to respective terminals Nand V, the input timing terminals for a register (bi-stablemultivibrator) on the trigger board.

Assuming an input signal on terminal N will set the register, anappropriate input signal applied to'terminal V will reset the register.Thus, every time a positive half cycle is applied to terminal N, theregister will go to a set condition, its transistor Q] will be turned onand its output junction A1 will go from positive to ground. Each timethe cycle signal applied to terminal V goes positive, transistor O2 isturned on and transistor Q1 is turned off, causing junction A2 to gofrom positive to ground and junction Al to go from ground to positive.

:Via differentiating capacitor-diode circuits 162 and 164, the negativegoing transitions appearing at junction A1 and A2 provide a signal waveform at junction A, having negative going timing spikes corresponding tothe beginning of each half cycle of the associated A.C. phase. Thenegative going timing pulses at junction A are used to control anintegrator reset circuit 166 which includes transistor 03. Viewing FIGS.2E and 3, each time a negative going spike appears at junction A, theintegrator reset transistor Q3 is turned on and provides a positivevoltage level (+l0V) at junction C which resets the threshold voltage ofintegrator 168 at that positive level. The integrator integrates from+10 to 10 Volts during the time period for a half cycle. The amplifiedspeed error control signal, from the up interlock circuit 108, which istransmitted on line 124 to terminal J, modifies the integrated saw toothvoltage output from integrator 168 at a summing junction E.

If the control signal applied to terminal J indicates a no powercondition, a fully amplified positive signal (e.g., +l0V in thisspecific case) from the safety interlock up circuit 108, that voltagelevel applied to summing junction E will keep integrated (saw tooth)voltage levels above ground level during the entire integrating period.Junction E is connected to the inverting input of an operational (highgain) amplifier 170 whose output has a range from negative (lOV) topositive (+l0V). As long as the voltage signal at junction E ispositive, the output of the comparator inverter 170 at junction G is atnegative saturation, i.e., lOV. Whenever the signal level at junction Egoes below zero to negative, the output of the comparator 170, junctionG, goes full positive (+l0V).

The wave form at the comparator output (junction G) is a square wave,the widths of the positive periods of which represent the desiredconduction angle with the time correlated A.C. half cycles in theassociated phase channel.

When the signal on input terminal J represents full power, (right handportion of FIG. 3), in other words, it is at its lOV level, theeffective integrated saw tooth wave form applied to comparator inverter170 is nega-.

tive during the entire integrating time period, causing the comparator170 to provide a fixed positive level output for the entire half cycletime period.

Any intermediate signal level applied to terminal J of the trigger boardwill modify the saw-tooth wave form at the summing junction E to formsomewhere between the full off and full on conditions shown in FIG. 3.The middle portion of the FIG. 3 chart shows an example of such anintermediate condition, a half conducting angle condition, wherein thezero Volt control signal at terminal J causes a wave form at junction Ewhich is negative during the last half of each half cycle. That negativeinput to the comparator 170 provides positive square waves on its outputto junction G during the last half of each cycle period.

The square wave signals from the trigger circuit comparator 170 areapplied through amplifier transistor Q4 and the resulting positive levelsignals on the emitter of Q4 are used to provide appropriately timedtrigger signals to both of the inverse parallel thyristors in anassociated thyristor switching device, e.g., device 76. The emitter ofO4 is connected to drive respective power amplifiers 172 (transistor Q)and 174 (transistor Q6) via a parallel input circuit. Transistor Q5 isinhibited by an Inhibit Gate 176 whenever the junction A is positive(during a negative half cycle of the associated A.C. phase) andtransistor Q6 is inhibited by an Inhibit Gate 178 whenever the junctionA is positive (during a positive half cycle of the associated A.C.phase). Power transistor Q5 can only be turned on during one (positive)half cycle of the associated A.C. phase and is only turned on during therelated period when the output transistor Q4 is on. Similarly, Powertransistor Q6 can only be turned on during the other (negative) halfcycle of the associated A.C. phase and is only turned on during therelated period when the output transistor Q4 is As shown in FIG. 3, theoutputs of power amplifiers 172 and 174 are square waves, the positivevoltage levels of which occur for desired, controlled periods duringassociated half cycles and always terminate at the end of a half cycle.As shown in FIG. 2E, the collectoremitter circuits of each poweramplifier transistor Q5 and O6 is series connected with the primarywinding of an associated isolation square wave transformer. Q5 operatestransformer 180 and Q6 operates transformer 182. The two leads of thesecondary winding of transformer 180 connect through plug boardterminals C and B to the trigger circuit of the half cycle (in theexample, the positive half cycle) switching thyristor 92 and the twoleads of the secondary winding of transformer 182 connect through plugboard terminals x and y to the trigger circuit of the other of the halfcycle (e.g., the negative half cycle) switching thyristor 90.

The isolation transformers 180 and 182 are square wave transformers andthusprovide square wave trigger signals to turn on the associatedthyristors 92 and 90 substantially instantaneously with the positivegoing transition of the isolation transformer output to its fullpositive voltage level, providing accurate control over desiredconduction angle of the associated phase half cycle.

The foregoing trigger circuit description was made in connection withthe up channel of phase C and shows how each half cycle of the A.C.phase wave in that channel will be controlled through its associatedthyristor to provide a conduction angle determined by the output signalfrom the trigger board comparator 170, as driven by the control signalon the up interlock output lines 122 and 124. The same control signal isused to drive the phase A up trigger board circuit 114 which, in accordwith phase A cycle timing signals, will trigger the inversed parallelthyristors 82 and 84 of the phase A up channel thyristor switchingdevice 74, at appropriate desired periods, within the positive andnegative half cycles.

If the interlock output control signal calls for down power the two downtrigger board circuits 116 and 120 will trigger their associatedthyristor devices in accord with associated phase cycle timing signals.

The three diodes 190, 192 and 194 seen in FIG. 2F, having their anodesrespectively connected to one of the input phases A, B and C and theircathode leads joined, constitute a clipper for attenuating over-voltagespikes.

Current limiting line chokes 140 and 142 are provided to protect thephase switching thyristors from excessive current surges.

The motor 60 can utilize an automatic cooling blower 150 or fan (FIG.2F) connected into the control circuit with desired automatic and safetyfeatures.

ALTERNATIVE EMBODIMENT THIRD PHASE CONDUCTION ANGLE CONTROL To providemore efficient power utilization by the three-phase motor 60, anadditional circuit (see FIG. 4) can be incorporated in the circuit shownin FIG. 2, to provide thyristor switching of third phase input to themotor, phase B in the exemplary disclosure. In FIG.

4, the added circuitry 200 is encircled in a dotted line box and only asmuch of the circuit of FIG. 2 which is needed to show the manner inwhich the third-phase control is connected, is shown outside of thedotted lines. The phase B input line is referenced as while othercomponents common to FIG. 2, retain the same reference characters,

The additional circuit 200 requires: (1) one trigger board, identifiedas trigger board N0. 5; (2) one thyristor switching device 202,including a pair of thyristors 204 and 206 connected in inverse parallelrelation between the phase B power input line 64 and the phase B motorlead 70; and (3) a blocking diode circuit 208 to provide a commoncontrol signal connection from both the up and down safety interlockcircuits 108 and 110 (FIG. 2D) to the No. 5 trigger board controlterminal J.

Because, when the three-phase power input to the motor 60 is reversed,the third power input line remains connected to the same motor inputconnection while the other two power line phase connections to the motorinputs are switched, one thyristor switching device 202 in the thirdphase channel can control conduction angle within that third phaseduring forward or reverse power input. Within the dual, inverse parallelthyristor device 202, the thyristor 204 controls phase B conductionangle for the positive half cycle and thyristor 206 controls phase Bconduction angle for the negative half cycle.

Still referring to FIG. 4, the trigger circuit 210 of trigger board No.5 is identical to that in the other trigger boards, as hereinbeforedescribed for trigger board No.'

4 (see FIG. 2E). Its terminals D, F, P, R and T connect to the samevoltage levels in the regulated power supply as do the same terminals ofthe other trigger boards. Terminals B and C provide trigger control ofthe positive half cycle thyristor 204 and terminals X and Y providetrigger control of the negative half cycle thyristor 206. Phase B cycletiming is derived on terminals N and V connected to the center tapsecondary on the phase B power supply transformer T shown in FIG. 2C.

As has been hereinbefore described, the system control signal whichindicates the required power input to motor 60 can be calling for up ordown power input regardless of the direction of rotation of the motor,i.e., whether the elevator is going up or down. The up signal and thedown signal are applied on two control signal lines 122 and 130respectively from the safety interlock circuits 108 and 110 (FIG. 2D).Because the single phase B trigger circuit 210 is used for both up anddown thyristor control in that phase, its input terminal J must beconnected to receive control signals from both the up and down controlsignal lines 122 and 130. That parallel connection is accomplished bythe blocking diode circuit 208 consisting of a diode 212 with itscathode connected to up signal line 122 and a diode 214 with its cathodeconnected to down signal line 130. The anodes of both diodes areconnected to terminal J of trigger board No. 5 which is also connected,through a dropping resistance 216, to a positive volt power supply.

With the aforedescribed third phase thyristor switching control, anyregulator (or error) signal from the control system amplifier 42 callingfor a desired motor speed will control thyristor firing in all threephase channels for a desired conduction angle. This provides bettercontrol and avoids undue heat losses which occur when the third phaseconduction angle is uncontrolled.

The various values of voltage resistance and capacitance in thedescribed embodiment are exemplary of an operative circuit and can bechanged in known manner by persons skilled in electronic circuitry andremain within the inventive concept.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A solid state trigger circuit to provide variable period outputsignals within a timed sequence of signals comprising: a bi-stablemultivibrator with inputs to each stage and an output from each stage;timing means, providing successive signals, alternately on saidmultivibrator inputs to oscillate said multivibrator at a desired timingrate, said multivibrator outputs being coupled to provide a voltagetransition spike at the start of each input signal; means responsive tosaid multivibrator output to provide a saw tooth wave form with periodscorresponding to said timing rate; means providing a linear voltageinput control signal indicative of a desired time period pulse width;and means comparing said control signal with said saw tooth wave formand providing corresponding square wave trigger output signals withsignal pulse periods equal to said desired pulse width, said voltagetransition signals from said multivibrator outputs control a thresholdreset circuit for the saw tooth wave generator and said reset circuitincludes a transistor having its collector connected to apply a presetvoltage level to the reset-terminal of the saw tooth generator and saidvoltage transition signals, via the multivibrator output, are applied tothe base of said transistor to control application of said presetvoltage level, said saw tooth generator is an integrator, saidtransistor is PNP, said voltage transistion signals are negative goingand said connection from said transistor collector terminal is to theintegrator inverting input enabling an integrator output with negativegoing integrating saw tooth wave forms, and wherein diode-capacitordifferentiating circuits couple said multi-vibrator outputs to providesaid combined output signal with transition spikes.

1. A solid state trigger circuit to provide variable period outputsignals within a timed sequence of signals comprising: a bi-stablemultivibrator with inputs to each stage and an output from each stage;timing means, providing successive signals, alternately on saidmultivibrator inputs to oscillate said multivibrator at a desired timingrate, said multivibrator outputs being coupled to provide a voltagetransition spike at the start of each input signal; means responsive tosaid multivibrator output to provide a saw tooth wave form with periodscorresponding to said timing rate; means providing a linear voltageinput control signal indicative of a desired time period pulse width;and means comparing said control signal with said saw tooth wave formand providing corresponding square wave trigger output signals withsignal pulse periods equal to said desired pulse width, said voltagetransition signals from said multivibrator outputs control a thresholdreset circuit for the saw tooth wave generator and said reset circuitincludes a transistor having its collector connected to apply a presetvoltage level to the reset terminal of the saw tooth generator and saidvoltage transition signals, via the multivibrator output, are applied tothe base of said transistor to control application of said presetvoltage level, said saw tooth generator is an integrator, saidtransistor is PNP, said voltage transistion signals are negative goingand said connection from said transistor collector terminal is to theintegrator inverting input enablIng an integrator output with negativegoing integrating saw tooth wave forms, and wherein diode-capacitordifferentiating circuits couple said multi-vibrator outputs to providesaid combined output signal with transition spikes.